Latest / Short Machshava On The Daf by Rabbi Yechezkel Hartman
Bava Basra 163: The Five Sources of the Letters
And the reason Dalet and Teis are interchangeable.
Source Sheet: https://res.cloudinary.com/ouinternal/image/upload/outorah%20pdf/ea3vmcz44mqsmgjc3tk7.pdf
The skinny
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